Method for controlling a yarn storage and feeding device, and yarn storage and feeding device

ABSTRACT

In a method for controlling a yarn storage and feeding device, particularly for a mechanical loom, comprising a storage surface adapted to have windings of a yarn wound thereonto and withdrawn therefrom by a consumer, and a control unit for a winding drive mechanism operable to adjust the winding speed in accordance with the consumption rate and in response at least to the actual value of the number of yarn windings on the storage surface, for adjusting the actual value towards a predetermined desired value, the desired value is altered in response to at least one alteration of the winding speed to thereby obtain an optimum smallness of the yarn supply on the storage surface. In a yarn storage and feeding device for performing this method, the control unit cooperates with a reference value memory (18) for the supply of desired values (nV) varying in a predetermined manner.

FIELD OF THE INVENTION

The present invention relates to a method for controlling a yarn storageand feeding device, and to a yarn storage and feeding device suitablefor performing the above method.

BACKGROUND OF THE INVENTION

According to EP B1 01 74 039, the winding speed at which yarn is woundonto the yarn storage surface is adjusted in accordance with thedifference between a predetermined desired value and an actual value ofthe number of yarn windings supported on the storage surface, and insuch a manner, that this difference varies within a limited rangebetween a positive value and a negative value. The desired valuecorresponds to the number of yarn windings required for satisfying amean consumption. Although in this case a low winding speed incombination with a low mean consumption results in the creation of asuitably adapted yarn supply, a yarn supply of the same magnitude is notrequired at higher winding speeds. In the case of a state of equilibriumbetween the winding speed and the mean consumption, an increase of theyarn consumption at higher winding speeds results in that the yarnsupply is replenished at a faster rate than in the case of lower windingspeeds, due to the high-speed operation of the winding drive mechanism.An excessive yarn supply is undesirable, however, particularly in thehigher winding speed range, because the danger of windings being woundupon one another is increased, and because the winding speed during thereplenishment of the yarn supply to an unnecessary size tends to becomeexcessive. Also during the replenishment of the yarn supply to anunnecessary size, the adaptation of the winding speed to a new state ofequilibrium after a change of the consumption takes a long time, andexcessive speed results in an undesirable increase of the mechanicalstress acting on the yarn, involving the danger of yarn breakage,particularly at the yarn supply side. Also the size of the yarn supplycan be further and excessively increased, proceeding from the alreadyunnecessarily great yarn supply, in the case of a delay caused by adecrease of the yarn consumption. The great number of windings in theexcessively great yarn supply hampers the advance of the yarn supply.The temporarily excessive speed and the mostly excessive yarn supplyalso result in an unnecessary energy consumption.

It is an object of the invention to provide a method and a yarn storageand feeder device to thereby ensure the presence of a yarn supply ofoptimum magnitude on the storage surface.

These objects are attained according to the invention by a method anddevice having the characteristics set forth below.

Both in the case of the method and of the device, the proposed object issimply attained by the consideration that, in the case of higher windingspeeds, the winding drive mechanism is capable in response to anincrease of consumption of replenishing the yarn supply to the necessarysize more rapidly than in the case of lower winding speeds, and thatwithout the danger of the yarn supply being completely depleted, so thatthe yarn supply can be smaller at higher winding speeds than at lowerwinding speeds. This is brought about by respective changes of thedesired value. In the case of a decrease of consumption, the change ofthe desired value prevents the size of the yarn supply from beingundesirably increased, the selected desired value being effective toadjust the yarn supply to the minimum size required for the reducedconsumption. The manner in or the law by which the desired value isvaried is at least in part dependent on the capacity of the windingdrive mechanism, which may be represented by a known characteristiccurve specific to the respective device. This characteristic curve mayfor instance be the acceleration curve of the winding drive mechanism.The consumption, or the characteristic of the consumption, respectively,is likewise of importance with regard to the variation of the desiredvalue. It is to be preceeded from the assumption, however, that the yarnstorage and feeding device is a priori matched to the consumer in such amanner that a reliable yarn supply is ensured under any operativeconditions to be expected. The variation of the desired value is ofparticular importance not only during normal operation, but also in thestarting phase and in the run-out phase down to the stopped condition,because under these circumstances the desired value plays an importantrole by preventing the occurrence of excessive speeds, and the formationof an excessive yarn supply in the run-out phase, respectively. Thereduction of the yarn supply to its optimum size for any consumptionrate results in various advantages. In the first place, the adjustedsize of the yarn supply reduces the danger of windings being wound uponone another. The drag forces opposing the advance of the yarn supply areconsiderably reduced. Furthermore there results a reduced maximum speedof the winding drive mechanism, because in the case of an increasedconsumption rate the winding speed will no longer become excessive tothereby create the unnecessarily great yarn supply for this high windingspeed. By the avoidance of such excessive speeds the mechanical stressacting on the yarn, particularly on the supply side, is reduced, withthe resultant reduction of the danger of yarn breakage at this location.The formerly unavoidable swinging adjustment of the winding speedtowards equilibrium with the consumption rate is eliminated, because thewinding speed is adjusted in harmony to the consumption rate with theaid of the desired values. The elimination of the swinging adjustmentresults in the applicable state of equilibrium being attained veryquickly. After the winding speed has been reduced in response to theconsumption rate, the size of the yarn supply is immediately matched tothe new consumption rate, because the winding speed is matched to theconsumption rate without any noticeable swinging adjustment as a resultof the variation of the desired value.

In summary, the method according to the invention and the constructionof the yarn storage and feeding device result in an improved quality ofthe yarn feeding process with improved energy husbandry and reduceddanger of malfunction.

One embodiment of the method permits the optimum small size of the yarnsupply to be obtained in each case in a simple manner. The higher thewinding speed at a given state of equilibrium, the smaller is the yarnsupply. Since the variation of the desired value is brought about in anautomatic manner, there is no need for external intervention.

Another provision takes into account that a relatively great yarn supplyis required at lower winding speeds, because in the case of an increaseof the consumption rate the winding drive mechanism is only capable ofreplenishing the supply at a slow rate.

A starting number can be established in view of the fact that thewinding drive mechanism, proceeding from the stopped condition, requiresa relatively long time for building the yarn supply up to the necessarysize in the case of an increase of the consumption rate. The startingnumber may thus correspond to the desired value for the slowest windingspeed (standstill). It is also conceivable, however, to select a higherstarting number, and to commence the adjustment of the winding speed inaccordance with the variation of the desired value only after apredetermined winding speed or a state of equilibrium has been attained.The starting number is also required for the initial establishment ofthe yarn supply. Under the assumption of a known and substantiallyconstant mean consumption rate, the desired objective can also beattained with at least one alteration of the desired value, i.e. byapplying to the control unit at least one desired value different fromthe starting number and matched to the known mean consumption rate, tothereby ensure that the yarn supply at this mean consumption rate is ofoptimum smallness, i.e. smaller than during the start-up phase. Therespective desired value, or rather the alteration of the desired value,preferably comes into effect with regard to the control function whenthe state of equilibrium has been attained after the start-up phase ofthe drive mechanism. In this manner it is possible to suppress aswinging adjustment phase, because this adjustment of the winding speedis carried out soon after leaving the starting number by matching thewinding speed to the desired value.

When the control of the winding speed according to the desired values iseffective to always ensure the optimum smallness of the yarn supply, andthe winding speed control process proceeds in a harmonic manner, theresult is a limitation not only of the mechanical stresses acting on theyarn, but also the variations of the yarn tension on the supply side.

The characteristic acceleration curve of the winding drive mechanism isa very useful point of departure for determining the different desiredvalues. This is because the speed at which the yarn supply isreplenished or diminished is to a large extent dependent on theacceleration and/or deceleration response of the winding drivemechanism. This proceeds from the assumption that the actual diameter ofthe storage surface, which may also be adjustable, or the yarn qualityare only of secondary importance.

The desired value may be determined in accordance with the known meanconsumption rate, i.e. the desired value is either calculated orempirically determined and applied to the control unit for use in itsoperation.

One manner of conducting the method permits a very fine control functionto be achieved. The frequency at which the information comparison isrepeated depends on the actually given operating conditions. Thisfrequency may also be selected to be higher or lower, for instance bymeans of an adjustable clock generator for the control unit.

Of particular advantage in this context is the performance of the methodusing a closed control loop, because the closed control loop, which isdominated by the desired values acting as reference values, permits avery fine control function to be achieved.

In the yarn storage and feeding device according to the invention, thespeed control function of the control unit is influenced by a referencevalue memory so as to establish and maintain the optimum smallness ofthe yarn supply at any winding speed value. Since the operation of thecontrol unit is governed by the desired values, an increase of thewinding speed to excessive values in response to an increase of theconsumption rate is avoided in the same manner as an undesirableincrease of the size of the yarn supply in response to a reducedconsumption rate. The mechanical stresses acting on the yarn are thusmaintained as small as possible. The optimum smallness of the yarnsupply in each winding speed range notwithstanding, the completeexhaustion of the yarn supply in response to an increase of theconsumption rate is reliably avoided.

The acceleration curve of the winding drive mechanism is a knownreference line and as such is useful for calculating or determining thedesired values.

A further advantageous embodiment includes a microprocessor in thecontrol unit and detector means acting to supply the control unit withinformations relating to the number of windings as wound and the numberof windings as consumed, and further relating to at least one desiredvalue. The microprocessor is suitably informed of the actual value in ananalogous process, for instance by counting the yarn windings. Undercertain conditions it could be sufficient to detect the actual value bydirectly scanning the storage surface by means of a plurality of yarndetectors, preferably at least three yarn detectors, to thereby createnear-analogous information for the control unit. The microprocessor inthe control unit is charged with an additional function, which however,it is capable of performing without any problem. The winding speed isadjusted in accordance with the desired values in such a manner that athigher winding speed values the size of the yarn supply is reduced atthe same rate as the increased speed permits the winding drive mechanismto replenish the yarn supply more rapidly. Also in the case of a reducedconsumption rate, the microprocessor acts to ensure that the yarn supplyis not undesirably increased.

In one embodiment, a tabular memory stores the desired values in theform of a sequence, which may be of a density practically resulting in acontinuous desired-value curve. A reading pointer is adjustable inaccordance with the winding speed to read only a respective one of thedesired values at any time and to transmit the information derivedtherefrom to the control unit. For applications of a more simple natureit is also sufficient, however, to provide the desired values at greaterintervals, so that only selected winding speed values are concerned,with significant desired-value changes occurring therebetween. In thecase of a known mean consumption rate, a single stage may be sufficient,i.e. the then applicable desired value is matched with this consumptionrate.

A further alternative embodiment switches from one yarn detector to thenext automatically, which results in the associated new desired valuebecoming effective. The result, however, is a desired-value curve with anumber of steps in the course of the curve corresponding to the numberof yarn detectors. This is quite sufficient, however, for attaining thedesired objective, particularly when there is a great number of suchdetectors. The spacings between the individual yarn detectors may beindividually adjustable. It is thus not necessary to select accuratelyequal spacings.

If the yarn detector is adjusted in the longitudinal direction of thestorage surface in accordance with the winding speed, this adjustmentresults in a variation of the desired value determining the function ofthe control unit for the adjustment of the winding speed.

In another embodiment, the desired value is electronically varied byadjusting the limited active detecting section of a wide-band detector.In a simplified form it would even be sufficient to provide a wide-banddetector with a longitudinally displaceable shutter opening permittingthe location whereat the wide-band detector scans the storage surface tobe displaced in response to variations of the winding speed, to therebyvary the desired value.

Association of the desired values to winding speed values selected atuniform intervals is favourable for obtaining a stable control response.

Since the capability of the winding drive mechanism of replenishing theyarn supply more rapidly at higher winding speeds than at lower windingspeeds may vary in accordance with the speed in a non-linear proportion,in the range of the lower winding speed values the differences betweenthe desired values may be relatively small. The differences between thedesired values are then of course relatively greater at higher windingspeed values.

One embodiment includes a particularly simple construction permittingthe desired value corresponding to the known mean consumption rate to beapplied to the electronic control unit in a particularly simple manner.The desired value can be individually adjusted and is automaticallyaccepted and used by the control unit for maintaining the yarn supplydesirably small during normal operation.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the subject matter of the invention shall now bedescribed by way of example with reference to the accompanying drawings,wherein:

FIG. 1 shows a diagrammatical side view of a yarn storage and feedingdevice,

FIG. 2 shows a diagram illustrating the development of desired values,

FIG. 3 shows a diagram illustrating alternative developments of desiredvalues,

FIG. 4 shows a diagram illustrating the acceleration characteristic orthe speed curve, respectively, of a winding drive mechanism of a yarnstorage and feeding device,

FIG. 5 shows a diagrammatical illustration of the yarn storage andfeeding device of FIG. 1 during one operative phase,

FIG. 6 shows the device of FIG. 1 during another operative phase,

FIG. 7 shows a partial diagrammatical side view of another embodiment ofthe invention

FIG. 8 shows a partial diagrammatical side view of a further embodimentof the invention, and

FIG. 9 shows a further embodiment of the invention.

DETAILED DESCRIPTION

In a yarn storage and feeding device 1 as shown in FIG. 1, a yarn 2supplied from a (not shown) supply bobbin passes through an inlet end 3to be wound by means of a winding element 4 onto a stationary storagesurface 6 in the form of windings W. The number of windings W formingthe yarn supply is designated "n". Through an exit end 7 yarn 2 iswithdrawn over the free end of storage surface 6 by a consumer C, forinstance a mechanical loom. Winding element 4 is rotated at a windingspeed V by a winding drive mechanism 5. Drive mechanism 5 is operativelyconnected to a control unit 8 adapted to have signals of adiagrammatically indicated detecting device 9 and a detector element 10applied thereto.

Detecting device 9 (for instance a Hall element) may be operable tomonitor winding element 4, so that the passage thereby of windingelement 4 or yarn 2 results in at least one pulse being applied tocontrol unit 8, each such pulse representing for instance one winding Wof yarn 2. In a similar manner detector element 10 may be operable togenerate a pulse for each passage thereby of yarn 2 as it is beingwithdrawn. By comparison of these signals control unit 8 is capable ofdetermining the actual number n of the windings W on storage surface 6.It is conceivable that detecting device 9 comprises other (not shown)detecting elements for determining the number of yarn windings W or theaxial dimension of the yarn supply, respectively, in a near-analogousmanner and for supplying the respective informations to control unit 8.

Control unit 8 operates to match the winding speed V to the yarnconsumption, so that, after a state of equilibrium between the meanconsumption rate and the winding speed has been achieved, the length ofyarn 2 wound onto storage surface 6 per time unit (for instance m/min)accurately corresponds to the length of yarn unwound therefrom.

When yarn 2 is for instance a weft yarn for a mechanical loom, theoperating mode of the loom determines a mean consumption rate, since theweft yarn is withdrawn at regular, shorter or longer intervals (regularcolour change or plain weaving mode), or at irregular, shorter or longerintervals (free pattern weaving mode). Although during each weft cyclethe acceleration and deceleration of the weft yarn is greater than thepossible acceleration and deceleration of drive mechanism 5 asillustrated by the respective acceleration characteristic, control unit8 responds to the mean consumption rate in such a manner that drivemechanism 5 operates continuously at a relatively high speed in the caseof a high weft cycle frequency, and likewise continuously, although at acorrespondingly reduced speed, in the case of an irregular or lower weftcycle frequency. When the mean consumption rate is varied during normaloperation, control unit 8 operates to correspondingly adjust the windingspeed until a state of equilibrium is again achieved. Maintaining thisstate of equilibrium does not necessarily require the winding speed tobe altered for each weft cycle, because the adjusted winding speed issufficient for suitably replenishing the yarn supply during theintervals between weft cycles.

Since the state of equilibrium at a higher consumption rate and at ahigher winding speed requires the yarn supply to be replenished morerapidly than in the case of a lower mean consumption and a lower windingspeed, the control operation is carried out in such a manner that thesize of the yarn supply is reduced in response to increasing windingspeeds, and that at the same time it is ensured that the size of theyarn supply never drops below an operatively indispensable value as itis being consumed.

In the yarn storage and feeding device 1 of FIG. 1, the desired value nVfor the number of yarn windings W on storage surface 6 is varied inaccordance with variations of the winding speed V, as shown in FIG. 2,so that the desired value nV is reduced in response to an increase ofthe winding speed V, and increased in response to a decrease of thewinding speed. The diagram of the winding speed V over the number ofwindings W thus shows a desired-value curve 11 defined by points 12 andextending along an arc to the left from a desired value nST. Desiredvalue nST defines a starting number established in accordance with theacceleration characteristic of drive mechanism 5 and/or the maximumconsumption rate in such a manner that the yarn supply is just preventedfrom being completely exhausted during start-up from a winding speedZero. As indicated in FIG. 2 at nST', the starting number may also begreater, in which case control unit 8 considers the desired values ofcurve 11 only beyond a determined winding speed value and controls theoperation of drive mechanism 5 only beyond the respective winding speedvalue, and then in accordance with curve 11, to thereby adjust the yarnsupply to a predetermined smallness in accordance with the desiredvalues defined by points 12. For enabling control unit 8 in thelast-named case to adjust the number of windings to the starting numbernST', the device may be provided with a starting detector ST as shownfor instance in FIG. 5, this starting detector being adapted toparticipate in the control operation only during the starting phase orwhen an initial yarn supply is to be wound onto the storage surface.

The diagram shown in FIG. 3 is similar to the one depicted in FIG. 2,there being, however, only three points 12_(F3), 12_(F2) and 12_(F1) forthree predetermined desired values, resulting in a broken curve 11'. Thedesired values along this curve 11' are likewise capable of ensuringthat the size of the yarn supply is reduced with increasing windingspeed. Also shown in FIG. 3 is the alternative possibility of varyingthe desired value, proceeding from nST for the starting number, in onlya single step, to result in a lower desired value nC. In the presentcase, the vertical (dot-lined) curve representing the adjusted desiredvalue is determined in accordance with an approximately known andsubstantially constant mean consumption rate, to thereby ensure that theyarn supply is maintained as small as possible at this consumption rate(horizontal dotted line). Although the adjusted desired value nC isshown as proceeding from the winding speed zero, the control operationis only determined by the desired value nC after the start-up phase, sothat an oscillating adjustment control is substantially avoided. Thissimplified solution is useful for instance in colour change and/orirregular colour change weaving operations. The desired value nC isdirectly applied to control unit 8, for instance by means of a codeswitch.

In this case the desired value is individually adjustable prior to beingprocessed by the control unit, preferably in an automatic manner.

Curve 11 in FIG. 2 may for instance be derived from the accelerationcharacteristic 13 of drive mechanism 5 shown in FIG. 4 with reference toa specific drive motor. As shown in FIG. 4, the acceleration curveinitially rises relatively steeply and is then gradually flattened toreach a maximum winding speed of 6250 rpm corresponding to about 500m/sec. The shape of curve 11 shown in FIG. 2 can be determined inaccordance with the shape of curve 13 in FIG. 4. Curve 11 may even be amathematically representable function of curve 13.

In the specific embodiment to which FIG. 2 relates, the desired value nVfor the number of windings W on storage surface 6 is onlyinsignificantly reduced at low winding speeds, the reduction of thedesired values increasing at higher winding speeds. The pointsrepresenting the respective desired values on curve 11 or curve 11',respectively, may be calculated or even empirically determined.

FIGS. 5 and 6 illustrate the method for controlling the yarn storage andfeeding device 1 of FIG. 1 in two operative phases during normaloperation, in each case in the presence of a state of equilibriumbetween the means consumption rate and the winding speed, i.e. in astate in which the number of windings wound onto storage surface 6 pertime unit corresponds to the number of windings withdrawn therefrom pertime unit.

As shown in FIG. 5, drive mechanism 5 and winding element 4 rotate at awinding speed value V1. Consumption monitoring detector 10 is connectedto control unit 8 by a control lead 14. Detector device 9 may comprise adetector for monitoring the movement of winding element 4 and applyingcorresponding signals to control unit 8 via a lead 15. The informationrelating to the winding speed value V1 is also applied to control unit 8via a control lead 16. This information might also originate fromdetector device 9 or from drive mechanism 5, to which control unit 8 isoperatively connected via a lead 17. Control unit 8 contains amicroprocessor MP capable of determining the actual value of the numberof windings from the informations applied thereto.

Control unit 8, or its microprocessor MP, respectively, contains atabular memory 18 in which the desired values nV are stored atpredetermined locations, for instance in the form of a diagram 19corresponding to the curve shown in FIG. 2. A dash-dotted line 20 inFIG. 5 represents a reading pointer associated to tabular memory 18 andadjustable in accordance with the winding speed to thereby readpredetermined locations of tabular memory 18 at correspondinglypredetermined winding speed values, so that for instance the desiredvalue nV1 is applied to microprocessor MP in the presence of windingspeed value V1. By comparison of the informations applied thereto,microprocessor MP determines whether the actual value corresponds to thedesired value nV1, this latter value denoting the axial position of thelast winding W of the yarn supply on storage surface 6 in the embodimentshown in FIG. 5. If the result of this comparison is zero or a valuelying within an admissible tolerance range, the previous winding speedV1 is maintained. If on the other hand the comparison of informationsshows an excessive deviation, control unit 8 operates to accelerate ordecelerate drive mechanism 5 to thereby adjust the actual value towardsthe desired value. This comparison of informations is repeated atpredetermined intervals, under the control for instance of a clockcircuit associated to microprocessor MP.

In the state shown in FIG. 6, the comparison of informations is carriedout at a higher winding speed value V2, in response to which the smallerdesired value nV2 is read from tabular memory 18. In this figure it isshown that the yarn supply at the winding speed V2 is smaller than inthe state shown in FIG. 5.

If the result of the comparison of informations is zero or a valuewithin an admissible tolerance range, the actual winding speed V2 ismaintained. If on the other hand the result shows an inadmissibledeviation, control unit 8 operates to adjust the winding speed to ahigher or lower value, and to carry out further comparisons ofinformations to thereby match the actual value with the desired value.

In summary, the control unit controls the winding speed in accordancewith the desired values to thereby maintain an optimum smallness of theyarn supply at least at selected winding speed values.

The control operation is carried out in a closed control loop, with thedesired values acting as reference values for the control operation. Inthe embodiment described above with reference to FIGS. 1 to 6, thedesired value is varied as a fictitious quantity, without determiningthe actual value by directly scanning the yarn supply on the storagesurface.

In the embodiment shown in FIG. 7, a longitudinally extending guide 21associated to storage surface 6 carries a narrow-range yarn detector 23for displacement therealong parallel to storage surface 6. Yarn detector23 is coupled to a drive spindle 22 operatively connected to anadjustment drive mechanism 24. The operation of adjustment drivemechanism 24 is controlled via a control lead 25--either through controlunit 8 or directly--in accordance with the winding speed of windingdrive mechanism 5 in such a manner that the distance s between yarndetector 23 and the inner end of guide 21 is a function of the actualwinding speed V2. When the winding speed is increased, yarn detector 23is displaced towards the inner end of guide 21; if on the other hand thewinding speed is reduced, yarn detector 23 is displaced in the oppositedirection. Yarn detector 23 is operatively connected to control unit 8of drive mechanism 5 via a control lead 26. In a conventional andtherefore not shown manner control unit 8 operates to control thewinding speed of winding element 4 in such a manner that the size of theyarn supply always corresponds to a desired value associated to arespective winding speed, the size of the yarn supply being determinedby the actual distance between yarn detector 23 and the inner end ofguide 21.

In the embodiment according to FIG. 7, the control operation may becarried out on the basis of the varying desired value and with referenceto the analogous actual value, similar to the manner illustrated inFIGS. 5 and 6.

In FIG. 7 it is important that the adjustment drive mechanism 24 isoperable to displace yarn detector 23 not in a linear relationship, butrather at an increasing rate towards the inner end of guide 21 inaccordance with the increase of the winding speed.

In the embodiment according to FIG. 8, the operation of whichcorresponds to the diagram (solid-line curve 11') of FIG. 3, guide 21carries three yarn detectors F1, F2 and F3 secured thereto atlongitudinal spacings parallel to storage surface 6. A commutator switch27 is provided for selectively connecting control lead 26 associated tocontrol unit 8 to any one of three control lead branches 26₁, 26₂ and26₃. A control lead 28 is provided for selectively operating commutatorswitch 27 in accordance with the winding speed of drive mechanism 5, sothat at any time only one of yarn detectors F1, F2 and F3 is operativelyconnected to control unit 8. As the winding speed increases, commutatorswitch 27 switches from yarn detector F1 to yarn detector F2, andsubsequently to yarn detector F3, in each case in the presence of apredetermined value of the winding speed. At the winding speed V2 asshown in FIG. 8, yarn detector F2 is activated. The signals generated byyarn detector F2 are used by control unit 8 for maintaining the lastwinding of the yarn supply at the location of yarn detector F2, inaccordance with the desired value nV2 associated to the winding speedV2. For adapting the device to different operating conditions, the yarndetectors can be individually adjusted along guide 21. It is alsopossible to provide more than three yarn detectors for permitting afiner graduation of the desired values.

Referring to FIG. 9, it would also be conceivable to provide a fixedlyinstalled wide-band detector 9', preferably a so-called CCD-opto-sensoror a photocell matrix for monitoring the yarn supply as a whole or atleast a major part thereof adjacent the exit end of the device, and toelectronically control the wide-band detector in such a manner that anactive detecting section thereof is displaced within the detecting range30 in the sense of a reduction of the yarn supply in response to anincrease of the winding speed. A similar effect could be produced by thedisplacement of a shutter-opening 35 in front of the wide-band detector9' as indicated by arrow 37.

In all of the embodiments described, the size of the yarn supplyrequired at a state of equilibrium between the mean consumption rate andthe winding speed is reduced in response to an increase of the windingspeed, to thereby exploit the effect that the winding drive mechanismcan replenish the yarn supply more rapidly at higher winding speeds thanat lower winding speeds. By the establishment of a desired value for thesize of the yarn supply and the reduction or variation of the desiredvalue in accordance with the variation of the winding speed, this isaccomplished either by electronic operations in the control unit or in asemi-mechanical process with the aid of correspondingly adjustable orselectively operable detector means.

We claim:
 1. A method for controlling a yarn storage and feeding device,said device comprising a storage surface on which the yarn can be woundin windings and from which the yarn can be withdrawn intermittently by aconsumer, a winding drive for winding the yarn onto the storage surface,and a control unit for controlling the winding drive, said control unitbeing operable to adjust the winding speed of the winding drive as afunction of the yarn consumption represented by the actual number ofwindings on the storage surface to adjust said actual number of windingsto a predetermined desired value, the method comprising the stepsof:detecting the actual number of windings on the storage surface andthe winding speed of the winding drive; achieving a state of approximateequilibrium between the number of windings being wound on said storagesurface and the number of windings being consumed, including the stepsof increasing the winding speed if the actual detected number ofwindings is smaller than said desired value and decreasing the windingspeed if the actual number of windings exceeds said desired value;presetting said desired value and presenting it in signal form to thecontrol unit; and altering said desired value to another desired valuein response to a detection of a change in the winding speed so that saidstate of approximate equilibrium will be achieved at a different numberof windings than with said first-mentioned desired value.
 2. A methodaccording to claim 1, wherein said step of altering the desired valueincludes at least one of the steps of lowering the desired value inresponse to an increase in winding speed so that said state ofapproximate equilibrium is achieved at a lower number of windings thanwith said first-mentioned desired value, and raising the desired valuein response to a decrease in winding speed so that said state ofequilibrium is achieved at a higher number of windings than with saidfirst-mentioned desired value.
 3. A method according to claim 2, whereinsaid step of altering the desired value is performed in an automaticmanner.
 4. A method according to claim 2, wherein said step of alteringthe desired value includes altering the desired value when the windingspeed exceeds a predetermined winding speed value.
 5. A method accordingto claim 2, wherein said presetting step includes setting saidfirst-mentioned desired value to a starting number of windings whichdepends on at least one of the yarn storing capability of the storagesurface and the yarn consumption capability of the consumer, and whereinsaid altering step includes stepwise altering the desired valueinversely to the winding speed as soon as said detected actual number ofwindings exceeds said starting number.
 6. A method according to claim 5,wherein said altering step includes altering the desired value inaccordance with a known average consumption of the consumer.
 7. A methodaccording to claim 2, wherein said presetting step includes setting saidfirst-mentioned desired value to a starting number which is determinedin accordance with at least one of an acceleration response capabilityof said winding drive and the maximum consumption capability of theconsumer.
 8. A method according to claim 2, wherein said altering stepincludes altering the desired value as a mathematical function of thewinding speed.
 9. A method according to claim 2, wherein the windingdrive has a known acceleration characteristic, said altering stepincluding altering the desired value as a function of the accelerationcharacteristic of said winding drive.
 10. A method according to claim 2,comprising the steps of associating different desired values to selectedwinding speed values, supplying said control unit with the respectivedesired value in response to the operation of the winding drive at oneof said selected winding speed values, and supplying said control unitwith the detected actual number of windings, said step of achievingapproximate equilibrium including comparing the desired value to saidactual number of windings, changing the winding speed in response to theresult of said comparing step, and repeating said comparing step inresponse to the operation of the winding drive at another one of saidselected winding speed values.
 11. A method according to claim 2,wherein said step of achieving approximate equilibrium includescomparing the desired value to the actual detected number of windings,and wherein said altering step and said detecting step and said step ofachieving approximate equilibrium are executed repeatedly to define arepetitively executed closed control loop wherein a current desiredvalue is compared to a current actual detected number of windings duringeach execution of the control loop, said detecting step includingcounting the windings being wound on said storage surface and thewindings being withdrawn by consumption from said storage surface.
 12. Ayarn storage and feeding device, comprising a yarn storage surface forstoring yarn windings thereon prior to ultimate withdrawal of the yarnwindings therefrom by a consumer, a winding drive mechanism for windingyarn onto said storage surface, and a control means for controlling thewinding speed of the winding drive mechanism in response to theconsumption of yarn by the consumer and according to at least onedesired value of the number of yarn windings desired to be stored onsaid storage surface in order to achieve a state of approximateequilibrium between the windings being wound on said storage surface andthe windings being withdrawn therefrom, said control means includingmeans for determining said desired value in response to the windingspeed so that the desired value is smaller the higher the winding speedis.
 13. A yarn storage and feeding device according to claim 12, whereinsaid desired value determining means includes a reference value memorymeans for storing therein a plurality of different winding speeds and aplurality of different desired values which correspond to the respectivewinding speeds and decrease in magnitude with increasing winding speedso that the desired value corresponding to a given winding speed issmaller the higher the winding speed is.
 14. A yarn storage and feedingdevice according to claim 13, wherein the magnitudes of said desiredvalues stored by said reference value memory means define a curve whichextends over an operational winding speed range of said winding drivemechanism and which is a methematical function of an acceleration curveof said winding drive mechanism.
 15. A yarn storage and feeding deviceaccording to claim 13, comprising a microprocessor in said control meansand comprising detector means for supplying said control means withinformation indicative of the number of windings wound on and of thenumber of windings consumed from said storage surface and of at leastone said desired value of the number of windings, said reference valuememory means comprising a readable memory in said microprocessor forstoring a plurality of winding speed-dependent desired values, saiddesired value determining means including means for reading a desiredvalue from said memory at any selected winding speed value, saidmicroprocessor including means for determining an actual value of thenumber of windings on said storage surface on the basis of saidinformation, and means for comparing said actual value to the desiredvalue as read from said memory, and said control means including meansfor adjusting the winding speed based on said comparison between saidactual value and said desired value.
 16. A yarn storage and feedingdevice according to claim 15, wherein said memory is a tabular memoryhaving a plurality of storage locations for storing the desired values,said desired value determining means including an adjustable pointermeans for addressing the respective storage locations in response tovariations in the winding speed.
 17. A yarn storage and feeding deviceaccording to claim 13, wherein said desired values are respectivelyassociated to winding speed values selected at uniform intervals.
 18. Ayarn storage and feeding device according to claim 17, wherein theintervals between successive desired values within the plurality ofdesired values increase with increasing winding speed.
 19. A yarnstorage and feeding device according to claim 13, wherein said referencevalue memory means comprises a code switch means for permitting saiddesired value to be adjusted to an average consumption associated withthe consumer.
 20. A yarn storage and feeding device according to claim12, wherein said desired value determining means comprises more than twoyarn detectors which are distributed alongside said storage surface andare directed onto said storage surface, said yarn detectors beinglocated alongside said storage surface at respective positions whichpositionally correspond to respective predetermined desired values ofthe number of windings to be stored on said storage surface, andcommutator means for selecting respective ones of said yarn detectors inaccordance with the winding speed in order to switch from one desiredvalue to another in response to a variation of the winding speed.
 21. Ayarn storage and feeding device according to claim 12, wherein saiddesired value determining means comprises a yarn detector means forgenerating a signal when the actual number of windings on the storagesurface is approximately equal to the desired value, said yarn detectormeans including a yarn detector mounted for adjustment alongside saidstorage surface in a longitudinal direction thereof to adjustably definethe desired value, and an adjustment drive mechanism connected to saidyarn detector and operable to adjust said yarn detector longitudinallyalong said storage surface in dependence on variations in the windingspeed so as to alter the desired value by shifting the yarn detector inthe longitudinal direction alongside said storage surface upon actuationof said adjustment drive mechanism.
 22. A yarn storing and feedingdevice according to claim 12, wherein said desired value determiningmeans comprises a wide-band yarn winding detector having an activewinding detecting section extending in a longitudinal directionalongside said storage surface, said wide-band yarn winding detectorbeing one of a CCD-detector and a photocell matrix, the active windingdetecting section being limitable in length in the longitudinaldirection, and means for shifting the active winding detecting sectionwithin the wide-band detecting range in accordance with variations ofthe winding speed in order to alter the desired value of the number ofwindings on the storage surface.